Classification of Herbicides According to Chemical Family For

DOI: 10.1111/wre.12153

Classiﬁcation of herbicides according to chemical family for weed resistance management strategies – an update

A FOROUZESH*,EZAND*,SSOUFIZADEH† & S SAMADI FOROUSHANI* *Iranian Research Institute of Plant Protection, Agricultural Research Education and Extension Organization (AREEO), Tehran, Iran, and †Department of Agroecology, Environmental Sciences Research Institute, Shahid Beheshti University, G.C., P.O. Box 19835-196, Tehran, Iran

Received 24 January 2014 Revised version accepted 26 January 2015 Subject Editor: Enrique Barriuso, INRA, France

mechanisms of action. According to this study, these Summary moieties have been assigned to the names of chemical There are inaccuracies in the chemical families of the families and active ingredients are then classified WSSA and HRAC herbicide classification systems within the chemical families accordingly. This study which could limit their practical use in herbicide-based has 119 chemical families, compared with 145 in the weed management strategies. In essence, these inaccu- WSSA system and 58 in the HRAC system. A major racies could be divided into four parts: (i) the nomen- priority of this study is the number of active ingredi- clature of many of the chemical families is not correct, ents covered; we included 410 active ingredients with (ii) distinct active ingredients are grouped in same known mechanisms of action and herbicide groups, chemical families, (iii) many chemical families have more than 100 active ingredients more than the current been repeated in at least two modes of action/herbicide classification systems. Overall, this study provides bet- groups, and (iv) many active ingredients have not been ter opportunities for the management of resistance to assigned to chemical family, herbicide group or mode herbicides through the application of improved pure of action. The aim of this study was to revise the cur- and applied knowledge. rent classifications and to propose corrections for the Keywords: herbicide resistance, cross-resistance, chemi- current ones. Detailed investigations on chemical cal structure, active ingredient, mode of action, Herbi- structure of the active ingredients of the registered her- cide Resistance Action Committee. bicides showed that some moieties have the same

FOROUZESH A, ZAND E, SOUFIZADEH S&SAMADI FOROUSHANI S (2015). Classiﬁcation of herbicides according to chemical family for weed resistance management strategies – an update. Weed Research 55, 334–358.

numerous studies about the advantages of rotational Introduction application of herbicide groups in delaying the evolu- Weed resistance to herbicides has become a major con- tion of herbicide-resistant weeds (Stephenson et al., cern in crop production worldwide that necessitates 1990; Gill, 1995; Itoh et al., 1999; Singh et al., 1999; special attention. Resistance to herbicides is often Hartmann et al., 2000; Legere et al., 2000; Hashem attributed to lack of rotational programmes of herbi- et al., 2001; Schmidt et al., 2004). Thus, a true under- cides and to continuous applications of herbicides with standing of the sites of action of herbicides is essential the same sites of action (Beckie et al., 2006). There are for strategic planning of herbicide-based weed control.

Correspondence: Saeid Souﬁzadeh, Department of Agroecology, Environmental Sciences Research Institute, Shahid Beheshti University, G.C., P.O. Box 19835-196, Tehran, Iran. Tel: (+98) 21 2990 2867; Fax: (+98) 21 2990 2867; E-mail: s_souﬁ[email protected]

An effective way to design a good rotational herbi- As a result, the names of some chemical families (as it cide programme would be to use classification systems stems from the active ingredients) are partially or thor- of these chemicals. Currently, there are two systems of oughly revised. Addition of more than 100 active classification for herbicides: one that belongs to the ingredients may also be an important step towards WSSA (2007) and the other that has been developed decreasing the occurrence of herbicide resistance. by the HRAC (2010). The former classification system uses numbers, whilst the latter uses letters for classify- Chemical basis of this study ing herbicides. Generally, the WSSA system includes 200 active ingredients and 145 chemical families and The basis of the new classification system relies on the the HRAC system covers 291 active ingredients fact that it is the active ingredient that determines its grouped in 58 chemical families. However, these two respective chemical family and ultimately the mecha- systems both have problems with the designation of nism of action it demonstrates (or it should be grouped chemical families that have negative implications for in). However, less familiarity with rules that govern chemical management of weeds. In a broad sense, we the nomenclature of organic compounds is the main divide these difficulties into two aspects. From a chem- cause of mistakes that exist in the HRAC and WSSA istry point of view, (i) there are many active ingredi- classifications. Some examples will be given to clarify ents with unknown chemical family, (ii) there are some this. Chemical family aryloxyphenoxypropionate mistakes in the nomenclature of chemical families, and (WSSA group 1 and HRAC group A) exist in both (iii) some active ingredients have been grouped in a classifications. This chemical family includes some chemical family when they are distinct. In the latter aromatic active ingredients, for example clodinafop, fe- case, such an issue may result in incorrect decision- noxaprop, fluazifop, haloxyfop, propaquizafop and making over the selection of herbicides to be used in a quizalofop. However, the correct name should be hy- rotational programme. As an example, if two distinct droxyphenoxyisopropionic acid. The justification is active ingredients are grouped in the same chemical that according to IUPAC (1979), the term ‘aryl’ refers family, it may be incorrectly inferred that as these two to a univalent aromatic hydrocarbon that only con- active ingredients are members of a same chemical tains carbon and hydrogen atoms. However, in the family, they will show the same cross-resistances. From current classification systems, the term ‘aryl’ has been a weed management point of view, there are 100 active used for aromatic compounds that also contain other ingredients that have not been assigned to any mecha- chemical elements other than carbon and hydrogen, nism of action, chemical family and herbicide group in such as nitrogen; using the term ‘aryl’ for a heterocy- both classification systems. This poses difficulties in clic aromatic compound is not correct. Also, according weed management programmes and could potentially to the WSSA and HRAC systems, the chemical family accelerate the occurrence of resistance. of the active ingredients clethodim and tralkoxydim Considering the shortcomings stated above, this from acetyl CoA carboxylase (ACCase) inhibitors is study aimed at revising the current classification sys- cyclohexanedione. Cyclohexane consists of a six-mem- tems, with the ultimate goals of correcting the record bered ring with six carbon atoms that are connected to and in supporting better planning of weed manage- each other with six single bonds, whilst such a chemi- ment strategies regarding rotational applications of cal structure belongs to cyclohexene. The difference herbicides. The objectives of this study can be summar- between cyclohexene and cyclohexane relates to the ised as follows: (i) corrections to be made in the replacement of a single bond by a double bond in the nomenclature of chemical families based on the rules ring of the latter. The suffix ‘-dione’ in cyclohexanedi- that govern organic chemistry, (ii) distinct active ingre- one indicates the replacement of two >CH2 groups by dients that have been grouped in one chemical family >CO in the ring, whilst in the active ingredients of this to be shifted to appropriate families, (iii) active ingre- chemical family, one >CH2 group is replaced by >CO dients with unknown chemical family and many active in the ring. Thus, the nomenclature of this chemical ingredients repeated with at least two mechanisms of family should be hydroxyoxocyclohexenecarbaldehyde action/herbicide groups to be assigned to appropriate oxime. As another example, 32 active ingredients chemical family and (iv) over 100 active ingredients within the photosystem II inhibitors have the moiety with known mechanisms of action, herbicide groups (moiety is a part of a molecule that may include either and chemical families to be added to both classification whole functional groups or parts of functional groups systems. The authors note that a mechanism of action as substructures; a functional group has similar chemi- directly depends on its active ingredient; thus, the cal properties whenever it occurs in different com- mechanism of action of most active ingredients can be pounds) triazinediamine and thus their chemical family identified merely on the basis of the chemical structure. in this study is named triazinediamine. Within the

Table 1 The numbers of mechanisms of action, herbicide groups, chemical families and active ingredients in each classiﬁcation system

Classiﬁcation systems Mechanisms of action HRAC groups WSSA groups Chemical families Active ingredients

This study 16 23 28 119 430 HRAC (2010) 16 23 26 58 291 WSSA (2007) 16 22 28 145 200

HRAC system, the name of the chemical family of the active ingredients within the chemical families has these active ingredients is triazine. Although triazine been based on their similarity regarding their moieties, exists in all active ingredients within this chemical fam- in some cases the nomenclature has not been solely ily, such a nomenclature is not correct because triazine based on the chemical structure of the moiety. How- also exists in some active ingredients of acetohydroxy ever, such an approach does not interfere with differ- acid synthase (AHAS) or acetolactate synthase (ALS) ences in the active ingredients and has been aimed at inhibitors. However, all 32 active ingredients within improving readability. photosystem II inhibitors have two amine groups in their chemical structure, and thus, the more appropri- Highlighting the differences between the ate nomenclature for the chemical family of these WSSA, HRAC and present classification active ingredients should be triazinediamine. systems One principle used in naming the chemical families in this study is as follows. Some active ingredients have As observed, this study has 119 chemical families com- different forms, such as acid or ester. An example is pared with 145 in the WSSA (2007) system and 58 in diclofop (acid form) and diclofop-methyl (ester form). the HRAC (2010) system (Table 1). In total, the pre- However, because different forms of a compound have sent study covered 430 active ingredients, which was the same mechanism of action (possibly with different 230 and 139 compounds more than the WSSA and degrees of effectiveness), where the moiety of the active HRAC systems, respectively. The number of chemical ingredient is an ester, the chemical family is named as families included in each mechanism of action in this an acid form, to prevent an excessive number of chem- study showed decreases, increases or no change com- ical families. Also, in the presented classification, only pared with the WSSA and HRAC systems (Table 2). the acid form of an active ingredient is mentioned, as The highest increases in number of families have been an example to show the position of an active ingredi- in the unknown, carotenoid biosynthesis inhibitors, ent within a mechanism of action, chemical family and photosystem II inhibitors, synthetic auxins and mitosis herbicide group. Also, although the classification of inhibitors. Compared with the WSSA system, most of

Table 2 The numbers of chemical families in each mechanism of action in different classiﬁcation systems

No. chemical families Mechanisms of action This study HRAC (2010) WSSA (2007)

Acetyl CoA carboxylase inhibitors 4 3 11 Acetolactate synthase or acetohydroxy 95 14 acid synthase (AHAS) inhibitors Photosystem ΙΙ inhibitors 21 11 30 Photosystem Ι inhibitors 1 1 4 Protoporphyrinogen oxidase 13 8 15 (PPG oxidase or protox) inhibitors Carotenoid biosynthesis inhibitors 13 1 20 Enolpyruvylshikimate-3-phosphate 21 1 synthase inhibitors Glutamine synthetase inhibitors 2 1 1 Dihydropteroate synthetase inhibitors 1 1 3 Mitosis inhibitors 18 11 15 Cellulose inhibitors 5 4 5 Oxidative phosphorylation uncouplers 1 1 1 Fatty acid and lipid biosynthesis inhibitors 3 4 6 Synthetic auxins 12 4 10 Auxin transport inhibitors 2 2 2 Unknown 12 0 7

Table 3 New active ingredients added to the HRAC (2010) classiﬁcation system with their corresponding chemical families, herbicide groups and mechanisms of action

HRAC WSSA Chemical families New active ingredients Mechanisms of action groups groups*

Hydroxyoxocyclohexen- Cloproxydim Acetyl CoA A1 ecarbaldehyde oxime carboxylase Hydroxyphenoxyisopropionamide Isoxapyrifop inhibitors Hydroxyphenoxyisopropionic acid Chlorazifop, Clofop, Fenthiaprop, Kuicaoxi, Trifop, Trifopsime Benzoyltriazinediol Triafamone Acetolactate synthase B2 Phenoxypyrimidinediol Pyribambenz-isopropyl or acetohydroxy Sulfonylurea Iofensulfuron, Metazosulfuron, acid synthase Methiopyrisulfuron, Monosulfuron, inhibitors Zuomihuanglong

Aminotriazinedione Ametridione Photosystem ΙΙ C1 5 Aminotriazinone Amibuzin, Ethiozin, Isomethiozin inhibitors Carbamoyloxycarbanilic acid Chlorprocarb, Phenisopham Phenyl aminopyridazone Brompyrazon Pyrimidinediamine Iprymidam, Tioclorim Triazinediamine Atraton, Aziprotryne = Aziprotryn, Chlorazine, CP 17029, Cyanatryn, Cyprazine, Dipropetryn, Eglinazine, Fucaojing, Ipazine, Mesoprazine, Methometon, Methoprotryne = Methoprotryn, Procyazine, Proglinazine, Sebuthylazine, Secbumeton, Simeton Uracil Isocil

Benzothiazolylurea Benzthiazuron C2 7 Chlorophenyl acrylamide Chloranocryl = Dicryl Chlorophenyl valeramide Erlujixiancaoan, Monalide Isoxazolylurea Monisouron Phenylthiourea Methiuron Phenylurea Bromuron, Buturon, Chloreturon, Defenuron, Difenoxuron, Fluothiuron, Metobenzuron, Monuron, Parafluron, Tetrafluron Thiadiazolylurea Buthiuron, Thiazafluron

Dihalohydroxybenzonitrile Bromobonil, Chloroxynil, Iodobonil C3 6 Pyridinium Cyperquat, Diethamquat, Morfamquat Photosystem Ι D22 inhibitors Nitrophenoxybenzene Chlornitrofen, Etnipromid, Fluorodifen, Protoporphyrinogen E14 Fluoronitrofen, Fucaomi, Furyloxyfen, oxidase (PPG Nitrofen, Nitroﬂuorfen oxidase or protox) Phenylpyrazole Nipyraclofen inhibitors Phenylpyrroledione Chlorphthalim, Flumipropyn Phenyltriﬂuoromethyluracil Flupropacil, Tiafenacil

Trifluoromethylphenoxy- Flufenican Carotenoid F1 12 pyridinecarboxamide biosynthesis Trifluoromethylphenyl - Metflurazon inhibitors aminopyridazone

Dioxocyclohexanecarbaldehyde Fenquinotrione, Ketospiradox F2 28 (27) Pyrazolecarbaldehyde Tolpyralate Phosphonomethylglycinamide Huangcaoling Enolpyruvylshikimate- G9 3-phosphate synthetase inhibitor Sulfanilylcarbamic acid Carbasulam, Fenasulam Dihydropteroate I18 synthetase inhibitors

Table 3 (Continued)

HRAC WSSA Chemical families New active ingredients Mechanisms of action groups groups*

Dinitroaniline Chlornidine, Dipropalin, Fluchloralin, Mitosis inhibitors K1 3 Isopropalin, Methalpropalin, Nitralin, Prodiamine, Proﬂuralin, Prosulfalin Phosphoramidothioic acid DMPA, Shuangjiaancaolin

Carbanilic acid Barban, BCPC, CEPC, Chlorbufam, K2 23 CPPC, Swep

Chloroacetamide Butenachlor, Allidochlor = CDAA, CDEA, K3 15 Delachlor, Diethatyl, Ethachlor, Ethaprochlor, Prynachlor, Terbuchlor, Xylachlor Sulfonylisoxazoline Fenoxasulfone Sulfonyltriazolecarboxamide Epronaz Trifluoromethanesulfonanilide Mefluidide, Perfluidone Dinitrophenol Dinofenate, Dinoprop, Dinosam, Etinofen, Oxidative M24 Medinoterb phosphorylation uncouplers Thiocarbamic acid Di-allate = Diallate, Ethiolate, Isopolinate, Fatty acid and lipid N8 Methiobencarb biosynthesis inhibitors Chlorobenzoic acid Tricamba Synthetic auxins O 4 Chlorophenoxyacetic acid 2,4,5-T, 3,4-DA, 4-CPA Chlorophenoxybutyric acid 2,4,5-TB, 3,4-DB, 4-CPB Chlorophenoxyisopropionic acid 3,4-DP, 4-CPP, Cloprop, Fenoprop Chlorophenylacetic acid Chlorfenac = Fenac Chlorophenylpropionic acid Chlorfenprop Chloropicolinic acid Halauxifen Chloropyrimidinecarboxylic acid Aminocyclopyrachlor Organic arsenic CMA, MAA, MAMA Unknown Z 17

*Group number enclosed in parenthesis is the new number suggested by WSSA (2011) instead of the adjacent number out of the parenthesis. the mechanisms of action showed decreases in their active ingredients, with known mechanisms of action number of chemical families. The number of chemical and HRAC and WSSA groups, to the current list of families in the unknown, mitosis inhibitors, synthetic active ingredients in HRAC and WSSA classifications. auxins, enolpyruvylshikimate-3-phosphate (EPSP) syn- For instance, the new active ingredient metazosulfuron thase inhibitors and glutamine synthetase inhibitors does not exist in HRAC (2010) and WSSA (2007) clas- increased, whilst numbers in the cellulose and auxin sifications. In this study and as a result of having the transport inhibitors, and oxidative phosphorylation un- same moiety with active ingredients within sulfonyl- couplers remained unchanged. urea chemical family, it has been grouped under Tables 3 and 4 show the active ingredients added to AHAS or ALS inhibitors from groups B (HRAC) & 2 the lists released by the HRAC and WSSA in 2010 (WSSA). Lee et al. (2011) also studied metazosulfuron and 2007 respectively. A marked increase in the num- for paddy weeds control and found it an efficient her- ber of active ingredients within the classification is bicide with very limited environmental side effects. The undoubtedly an important achievement of this study. obsolete herbicide chlorprocarb is an example of a her- As explained before, it is the chemical structure of the bicide where the mechanism of action of has not been active ingredient which determines its mechanism of identified to date. However, because chlorprocarb action. Based on this fact, detailed investigations on includes carbamoyloxycarbanilic acid, it could be chemical structure of the active ingredients of the regis- grouped as a photosystem II inhibitor, based on the tered herbicides showed that some moieties have same current approach to chemical family nomenclature. mechanisms of action. According to this study, these As shown, the present classification has 139 active moieties have been assigned to the names of chemical ingredients more than the HRAC system and 230 families and active ingredients are then classified within active ingredients more than the WSSA system. It the chemical families accordingly. Such a classification should also be noted that Table 3 only consists of method resulted in the addition of more than 100 those active ingredients for which an agreement exists

Table 4 New active ingredients added to the WSSA (2007) classiﬁcation system with their corresponding chemical families, herbicide groups and mechanisms of action

Mechanisms of HRAC WSSA Chemical families New active ingredients action groups groups*

Hydroxyoxocyclohexen- Cloproxydim, Profoxydim Acetyl CoA A1 ecarbaldehyde oxime carboxylase Hydroxyphenoxyiso- Isoxapyrifop inhibitors propionamide Hydroxyphenoxyisopr- Chlorazifop, Clofop, Fenthiaprop, Kuicaoxi, opionic acid Trifop, Trifopsime Benzoyltriazinediol Triafamone Acetolactate synthase B2 Phenoxypyrimidinediol Pyriminobac, Pyribambenz-isopropyl or acetohydroxy acid Phenylhydroxymeth- Pyrimisulfan synthase inhibitors ylpyrimidinediol Phenylthiopyrimidinediol Pyriftalid Sulfonylaminocarbony- Thiencarbazone-methyl ltriazolinone Sulfonylurea Iofensulfuron, Mesosulfuron, Metazosulfuron, Methiopyrisulfuron, Monosulfuron, Orthosulfamuron, Oxasulfuron, Propyrisulfuron, Tritosulfuron, Zuomihuanglong Triazolopyrimidinesulf- Metosulam, Pyroxsulam onamide

Aminotriazinedione Ametridione Photosystem ΙΙ C1 5 Aminotriazinone Amibuzin, Ethiozin, Isomethiozin inhibitors Carbamoyloxycarbanilic Chlorprocarb, Phenisopham acid Phenyl aminopyridazone Brompyrazon Pyrimidinediamine Iprymidam, Tioclorim Triazinediamine Atraton, Aziprotryne = Aziprotryn, Chlorazine, CP 17029, Cyanatryn, Cyprazine, Dimethametryn, Dipropetryn, Eglinazine, Fucaojing, Ipazine, Mesoprazine, Methometon, Methoprotryne = Methoprotryn, Procyazine, Proglinazine, Propazine, Sebuthylazine, Secbumeton, Simeton, Terbutryn = Terbutryne Uracil Isocil, Lenacil

Dibromohydroxybenzal- Bromofenoxim C3 6 dehyde oxime Dihalohydroxybenzonitrile Bromobonil, Chloroxynil, Iodobonil Phenylpyridazinol Pyridafol

Benzothiazolylurea Benzthiazuron C2 7 Chlorophenyl acrylamide Chloranocryl = Dicryl Chlorophenyl valeramide Erlujixiancaoan, Monalide, Pentanochlor = Solan Isoxazolylurea Isouron, Monisouron Phenylthiourea Methiuron Phenylurea Bromuron, Buturon, Chlorbromuron, Chloreturon, Chloroxuron, Defenuron, Difenoxuron, Fenuron, Fluothiuron, Metobenzuron, Metobromuron, Monuron, Neburon, Parafluron, Tetrafluron Thiadiazolylurea Buthiuron, Ethidimuron, Thiazafluron Pyridinium Cyperquat, Diethamquat, Morfamquat Photosystem Ι D22 inhibitors

Table 4 (Continued)

Mechanisms of HRAC WSSA Chemical families New active ingredients action groups groups*

Bipyrazole Pyraclonil Protoporphyrinogen E14 Nitrophenoxybenzene Chlomethoxyfen, Chlornitrofen, Etnipromid, oxidase (PPG Fluorodifen, Fluoronitrofen, Fucaomi, oxidase or protox) Furyloxyfen, Halosafen, Nitrofen, Nitrofluorfen inhibitors Phenylimidazolidinedione Profluazol Phenyliminothiadiazoline Thidiazimin Phenyloxazolidinedione Pentoxazone Phenylpyrazole Fluazolate, Nipyraclofen Phenylpyrroledione Chlorphthalim, Cinidon-ethyl, Flumipropyn Phenyltriazolinone Bencarbazone Phenyltrifluoromethyluracil Benzfendizone, Flupropacil, Saflufenacil, Tiafenacil Trifluoromethylphenox- Ethoxyfen ychlorobenzene

Trifluoromethylphenox- Flufenican Carotenoid F1 12 ypyridinecarboxamide biosynthesis Trifluoromethylphenyl Metflurazon inhibitors aminopyridazone

Dioxocyclohexanecarb- Fenquinotrione, Ketospiradox, Tefuryltrione, F2 28 (27) aldehyde Tembotrione Isoxazolecarbaldehyde Isoxachlortole Oxobicyclooctenecarb- Benzobicyclon, Bicyclopyrone aldehyde Pyrazolecarbaldehyde Pyrasulfotole, Tolpyralate Phosphonomethylglyci- Huangcaoling Enolpyruvylshikimate- G9 namide 3-phosphate synthase inhibitor Hydroxy methylphosphi- Bilanafos Glutamine synthetase H10 noylhomoalaninamide inhibitor Sulfanilylcarbamic acid Carbasulam, Fenasulam Dihydropteroate I18 synthetase inhibitors

Benzyl propionamide Tebutam = Butam Mitosis inhibitors K1 3 Dinitroaniline Butralin, Chlornidine, Dinitramine, Dipropalin, Fluchloralin, Isopropalin, Methalpropalin, Nitralin, Proﬂuralin, Prosulfalin Phosphoramidothioic Amiprophos, Butamifos, DMPA, acid Shuangjiaancaolin

Carbamoylmethylphos- Piperophos K3 15 phorodithioic acid Chloroacetamide Allidochlor = CDAA, Butenachlor, CDEA, Delachlor, Diethatyl, Dimethachlor, Ethachlor, Ethaprochlor, Pethoxamid, Propisochlor, Prynachlor, Terbuchlor, Xylachlor Diphenylacetamide Diphenamid Naphthoxyisopropio- Naproanilide namide Phenyloxotriazolinecarb- Ipfencarbazone oxamide Sulfonylisoxazoline Fenoxasulfone, Pyroxasulfone Sulfonyltriazolecarbox- Cafenstrole, Epronaz amide Trifluoromethanesulfo- Mefluidide, Perfluidone nanilide

Carbanilic acid Barban, BCPC, CEPC, Chlorbufam, K2 23 Chlorpropham, CPPC, Propham, Swep Dichlorobenzothioamide Chlorthiamid Cellulose inhibitors L 20 Phenyltriazolecarboxamide Flupoxam (28) Fluoromethyltriazined- Indaziﬂam, Triaziﬂam (29) iamine

Table 4 (Continued)

Mechanisms of HRAC WSSA Chemical families New active ingredients action groups groups*

Dinitrophenol Dinofenate, Dinoprop, Dinosam, Dinoseb, Oxidative M24 DNOC, Etinofen, Medinoterb phosphorylation uncouplers Thiocarbamic acid Di-allate = Diallate, Dimepiperate, Ethiolate, Fatty acid and lipid N8 Isopolinate, Methiobencarb, Orbencarb, biosynthesis Tiocarbazil inhibitors Dihydrobenzofuranyl Benfuresate 16 sulphonate Chlorobenzoic acid 2,3,6-TBA, Chloramben, Tricamba Synthetic auxins O 4 Chlorooxobenzothiaz- Benazolin olylacetic acid Chlorophenoxyacetic 2,4,5-T, 3,4-DA, 4-CPA acid Chlorophenoxybutyric 2,4,5-TB, 3,4-DB, 4-CPB acid Chlorophenoxyisopro- Clomeprop pionamide Chlorophenoxyisoprop- 3,4-DP, 4-CPP, Cloprop, Fenoprop ionic acid Chlorophenylacetic acid Chlorfenac = Fenac Chlorophenylpropionic Chlorfenprop acid Chloropicolinic acid Halauxifen Chloropyrimidinecarb- Aminocyclopyrachlor oxylic acid Chloroquinolinecarbox- Quinmerac ylic acid Organic arsenic CMA, MAA, MAMA Unknown Z 17 Benzanilide Etobenzanid 27 (26) Benzyl butyramide Bromobutide Benzyldihydrooxazinone Oxaziclomefone Benzylurea Cumyluron, Daimuron, Methyldymron Fluorenecarboxylic acid Chlorﬂurenol = Chlorﬂurecol Pelargonic acid Oleic acid Phenyl pyridylthiocarbamate Pyributicarb

*Group numbers enclosed in parenthesis are the new numbers suggested by WSSA (2011) instead of the adjacent number out of the parenthesis or they are being suggested for the first time (such as group number 29). on their mechanisms of action according to the HRAC classification, both active ingredients have been and WSSA. This is also a reason of why the number grouped in the triazinone chemical family. The suffix of new active ingredients in Table 3 does not match ‘-one’ in triazinone indicates the replacement of one with the corresponding number given in Table 1. Hav- >CH2 group by >CO in the triazine ring, whilst in hex- ing more active ingredients with known chemical fam- azinone, two >CH2 groups are replaced by >CO in the ily, mechanism of action and herbicide group (i) ring. Thus, attributing hexazinone to the triazinone increases the flexibility in designing herbicide rotational chemical family is not correct. Accordingly, the correct programmes and (ii) decreases the chance of occur- name for this compound is triazinedione. Such a mis- rence of cross-resistance. Knowing about herbicide take in the nomenclature of this chemical family has chemical family grouping could serve as a short-term resulted in classification of hexazinone and metribuzin strategy for managing resistance to site of action (Bec- in one chemical family. The considerable difference kie et al., 2006). between the resistance levels of these two herbicides To further explain the benefits of this study in terms (Table 5) in the study of Perez-Jones et al. (2009) of herbicide resistance management, we give some clearly shows that these two herbicides belong to dif- examples. The chemical families of active ingredients ferent chemical families. However, one interpretation hexazinone and metribuzin are aminotriazinedione and of the Perez-Jones et al. (2009) study is that these two aminotriazinone, whilst according to HRAC (2010) herbicides belong to a same chemical family, but they

Table 5 Comparison of the resistance level to selected herbicides in the chemical families of HRAC and this study

Chemical families Species Herbicides HRAC (2010) This study Resistance ratio References

Amaranthus hybridus (L.) Diuron Urea Phenylurea 1.4 Fuerst et al. (1986) Amach Tebuthiuron Thiadiazolylurea 22 Kochia scoparia (L.) Diuron Phenylurea 6.8 Mengistu et al. (2005) Schrad Tebuthiuron Thiadiazolylurea 37.7 Capsella bursa-pastoris Hexazinone Triazinone Aminotriazinedione 22.3 Perez-Jones et al. (2009) (L.) Medik Metribuzin Aminotriazinone 3.9 had shown different resistance levels. In the WSSA WSSA systems, respectively, which have mistakes in (2007) classification system, two and three chemical their nomenclature. Corrections were made based on families have been attributed to hexazinone and the chemical structure of the active ingredient. For metribuzin respectively. Such an uncertainty in chemi- instance, currently the chemical family of the active cal families does not allow their usage in resistance ingredients oxadiargyl and oxadiazon from studies, which may have implications for herbicide protoporphyrinogen oxidase (PPG oxidase or protox) resistance. As another example, according to HRAC inhibitors is oxadiazole. Oxadiazole consists of a five- (2010), the chemical family of active ingredients diuron membered ring with two carbon atoms, two nitrogen and tebuthiuron is urea, whilst this is not correct atoms and one oxygen atom that are connected to according to this study. Although urea exists in both each other by two double bonds and three single active ingredients, due to considerable differences in bonds. However, in the active ingredients of this fam- the chemical structure of these two active ingredients, ily, one >CH2 group is replaced by >CO in the ring. they are grouped in different chemical families in this Thus, the correct nomenclature for this compound is study. Significant difference between the resistance oxadiazolone. level of diuron and tebuthiuron (Table 5), as founded Another inaccuracy in the current classifications by Mengistu et al. (2005) and Fuerst et al. (1986), was that some chemical families were repeated in at clearly shows that these two herbicides do not belong least two mechanisms of action/herbicide groups, to a same chemical family. Such a great difference in whilst the active ingredients within a chemical family resistance level should not occur between herbicides of have only one mechanism of action/herbicide group the same chemical family. In this study, the presence (Tables 6 and 7). For instance, the substituted urea of urea in the chemical structure of the two active chemical family in the WSSA system has been repeated ingredients is not an acceptable reason for classifica- in groups 5 and 7 within photosystem II inhibitors, tion of these two active ingredients in a same family, which means that this chemical family has two sites of because urea alone does not result in a same mecha- action. The new classification and corrections of nism of action. In the WSSA (2007) classification, nomenclature have solved this issue. Another example three chemical families have been attributed to these is that fluometuron in the HRAC (2010) classification two active ingredients; thus one cannot use their chem- has two mechanisms of action, that is photosystem II ical families in resistance studies. As another example, inhibitor and carotenoid biosynthesis inhibitor. Fluo- active ingredient metoxuron from photosystem II meturon appears to be selectively toxic to one or more inhibitors has been classified under group 5 (C1 in light-mediated biochemical reactions required for the HRAC) in the WSSA 2007 classification system. This formation and function of photosynthetic pigments grouping has not been changed in the 2011 version of WSSA classification. However, this active ingredient is classified under group C2 (group 7 in WSSA) in Table 6 Chemical families repeated in two mechanisms of action HRAC 2010 classification system. According to this in the HRAC (2010) classification system study, this active ingredient contains the moiety phenylurea, and this moiety exists in groups 7 (WSSA) Chemical families HRAC groups and C2 (HRAC) in both classification systems. Thus, Benzamide K1 &L metoxuron should be classified under a same group. Benzoic acid K1 &O The mistakes in the nomenclature of the chemical Carbamate I & K2 families in the HRAC and WSSA systems are shown Diphenyl ether E & F3 Nitrile C &L in Tables S1 and S2 respectively. As observed, there 3 Triazolinone C1 &E are 17 and 27 chemical families in the HRAC and

Table 7 Chemical families repeated in at least two mechanisms and organelles (Sikka & Pramer, 1968). However, of action/herbicide groups in the WSSA (2007) classification according to the WSSA (2007) classification, being a system photosystem II inhibitor has only been accepted as the Chemical families WSSA groups valid mechanism of action for this active ingredient. On the other hand, further investigation of the chemi- Acetamide 7 & 15 Amide 3 & 7 & 12 & 14 & 15 & 21 cal structure of fluometuron shows that it includes the Anilide 1 & 12 & 15 phenylurea moiety. This moiety exists in some of pho- Arsenical 17 & 27 tosystem II inhibitor active ingredients. Thus, fluo- Benzonitrile 6 & 20 meturon may also have the same mechanism of action. Carbanilate 5 & 23 The difference between fluometuron and photosystem Nitrile 6 & 20 Nitrodiphenylether 11 & 14 II inhibitor active ingredients is the presence of a triflu- Nitrophenylether 11 & 14 oromethyl group in the former active ingredient. Thus, Organic arsenical 17 & 27 when WSSA, similar to HRAC, classified this active Organophosphorus 8 & 9 & 10 & 18 & 27 ingredient as a carotenoid biosynthesis inhibitor, we Phenylurea 5 & 7 can call its chemical family trifluoromethylphenylurea Pyrazole 2 & 14 & 15 & 27 & 28 with this mechanism of action. Also, as the chemical Pyridazinone 5 & 12 & 14 Pyridine 3 & 4 & 12 structure of parafluron and fluometuron is very similar Quaternary ammonium 22 & 27 to each other, it has the same mechanism of action Substituted amide 3 & 7 & 15 and group as fluometuron. Substituted urea 5 & 7 Classification of active ingredients within chemical Sulphonamide 2 & 18 families according to their chemical structure may Triazolone 2 & 14 Uracil 5 & 14 result in further understanding of the biochemical basis of active ingredients. For instance, the difference in

Table 8 Target-site (ALS/AHAS gene) herbicide resistance to ALS/AHAS inhibitors in the sulfonylurea herbicides

Mutation* Substitution Species Herbicides Resistance index† References

Asp 376 Glu Raphanus Chlorsulfuron VH Yu et al. (2012) raphanistrum L. Sulfometuron Pro 197 Leu Amaranthus Rimsulfuron M Sibony et al. (2001) retroflexus L. Tribenuron-methyl Triflusulfuron-methyl Amidosulfuron H Chlorimuron-ethyl Metsulfuron-methyl Nicosulfuron Sulfometuron-methyl Triasulfuron Chlorsulfuron VH Thifensulfuron-methyl Ser Bromus tectorum L. Primisulfuron Park & Mallory-Smith (2004) Sulfosulfuron Papaver rhoeas L. Chlorsulfuron L Duran-Prado et al., (2004) Metsulfuron-methyl Rimsulfuron H Sulfometuron-methyl Tribenuron-methyl Thr Lactuca serriola L. Chlorsulfuron VH Preston et al. (2006) Sulfometuron–methyl Triasulfuron Trp 574 Leu Amaranthus Nicosulfuron H Scarabel et al. (2007) retroflexus L. Oxasulfuron VH Thifensulfuron-methyl

*Amino acid number is standardised to the Arabidopsis thaliana sequence.

†Resistance index deﬁned as effective herbicide dose reducing growth or survival by 50% compared with the non-treated control (ED50) of the resistance compared with the susceptible biotype: L = low resistance (2–5), M = moderate resistance (6–10), H = high resistance (11–100) and VH = very high resistance (>100).

Table 9 Active ingredients of this study according to mechanism of action, herbicide group and chemical family

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

A Acetyl CoA Hydroxyoxocyclohexenecarbaldehyde Alloxydim, Butroxydim, 1 carboxylase oxime Clethodim, Cloproxydim, inhibitors Cycloxydim, Profoxydim, Sethoxydim, Tepraloxydim, Tralkoxydim

Hydroxyphenoxyisopropionamide Isoxapyrifop, Metamifop

Hydroxyphenoxyisopropionic acid Chlorazifop, Clodinafop, Clofop, Cyhalofop-butyl, Diclofop, Fenoxaprop-P, Fenthiaprop, Fluazifop-P, Haloxyfop-P, Kuicaoxi, Propaquizafop, Quizalofop-P, Trifop, Trifopsime Phenyloxopyrazolinyl formate Pinoxaden

B Acetolactate synthase Benzoyltriazinediol Triafamone 2 or acetohydroxy acid synthase inhibitors

Oxoimidazolinylbenzoic acid Imazamethabenz

Oxoimidazolinylnicotinic acid Imazamox, Imazapic, Imazapyr, Imazaquin, Imazethapyr

Phenoxypyrimidinediol Bispyribac, Pyribambenz- isopropyl, Pyribenzoxim, Pyriminobac

Phenylhydroxymethylpyrimidinediol Pyrimisulfan

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Phenylthiopyrimidinediol Pyriftalid, Pyrithiobac

Sulfonylaminocarbonyltriazolinone Flucarbazone, Propoxycarbazone, Thiencarbazone-methyl

Sulfonylurea Amidosulfuron, Azimsulfuron, Bensulfuron-methyl, Chlorimuron, Chlorsulfuron, Cinosulfuron, Cyclosulfamuron, Ethametsulfuron-methyl, Ethoxysulfuron, Flazasulfuron, Flucetosulfuron, Flupyrsulfuron- methyl-sodium, Foramsulfuron, Halosulfuron-methyl, Imazosulfuron, Iodosulfuron, Iofensulfuron, Mesosulfuron, Metazosulfuron, Methiopyrisulfuron, Metsulfuron-methyl, Monosulfuron, Nicosulfuron, Orthosulfamuron, Oxasulfuron, Primisulfuron, Propyrisulfuron, Prosulfuron, Pyrazosulfuron, Rimsulfuron, Sulfometuron, Sulfosulfuron, Thifensulfuron- methyl = Thiameturon-methyl, Triasulfuron, Tribenuron, Triﬂoxysulfuron, Triﬂusulfuron- methyl, Tritosulfuron, Zuomihuanglong Triazolopyrimidinesulfonamide Cloransulam, Diclosulam, Florasulam, Flumetsulam, Metosulam, Penoxsulam, Pyroxsulam

C1 Photosystem ΙΙ Aminooxotriazolinecarboxamide Amicarbazone 5 inhibitors

Aminotriazinedione Ametridione, Hexazinone

Aminotriazinone Amibuzin, Ethiozin, Isomethiozin, Metamitron, Metribuzin

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Carbamoyloxycarbanilic acid Chlorprocarb, Desmedipham, Phenisopham, Phenmedipham

Phenyl aminopyridazone Brompyrazon, Chloridazon = Pyrazon

Pyrimidinediamine Iprymidam, Tioclorim

Triazinediamine Ametryn = Ametryne, Atraton, Atrazine, Aziprotryne = Aziprotryn, Chlorazine, CP 17029, Cyanatryn, Cyanazine, Cyprazine, Desmetryn = Desmetryne, Dimethametryn, Dipropetryn, Eglinazine, Fucaojing, Ipazine, Mesoprazine, Methometon, Methoprotryne = Methoprotryn, Procyazine, Proglinazine, Prometon, Prometryn = Prometryne, Propazine, Sebuthylazine, Secbumeton, Simazine, Simeton, Simetryn = Simetryne, Terbumeton, Terbuthylazine, Terbutryn = Terbutryne, Trietazine Uracil Bromacil, Isocil, Lenacil, Terbacil

C2 Benzothiazolylurea Benzthiazuron, 7 Methabenzthiazuron = Methibenzuron

Chlorophenyl Chloranocryl = Dicryl acrylamide

Chlorophenyl Propanil propionamide

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Chlorophenyl Erlujixiancaoan, Monalide, valeramide Pentanochlor = Solan

Isoxazolylurea Isouron, Monisouron

Oxooxadiazolylphenylurea Dimefuron

Phenylthiourea Methiuron

Phenylurea Bromuron, Buturon, Chlorbromuron, Chloreturon, Chlorotoluron = Chlortoluron, Chloroxuron, Defenuron, Difenoxuron, Diuron, Fenuron, Fluometuron, Fluothiuron, Isoproturon, Linuron, Metobenzuron, Metobromuron, Metoxuron, Monolinuron, Monuron, Neburon, Parafluron, Siduron, Tetrafluron Thiadiazolylurea Buthiuron, Ethidimuron, Tebuthiuron, Thiazafluron

C3 Benzothiadiazinanonedioxide Bentazone = Bentazon 6

Dibromohydroxybenzaldehyde oxime Bromofenoxim

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Dihalohydroxybenzonitrile Bromobonil, Bromoxynil, Chloroxynil, Iodobonil, Ioxynil

Phenylpyridazinol Pyridafol, Pyridate

D Photosystem Ι Pyridinium Cyperquat, Diethamquat, Diquat, 22 inhibitors Morfamquat, Paraquat

E Protoporphyrinogen Bipyrazole Pyraclonil 14 oxidase (PPG oxidase or protox) inhibitors

Nitrophenoxybenzene Acifluorfen, Bifenox, Chlomethoxyfen, Chlornitrofen, Etnipromid, Fluorodifen, Fluoroglycofen, Fluoronitrofen, Fomesafen, Fucaomi, Furyloxyfen, Halosafen, Lactofen, Nitrofen, Nitrofluorfen, Oxyfluorfen Phenylimidazolidinedione Profluazol

Phenyliminothiadiazolidone Fluthiacet

Phenyliminothiadiazoline Thidiazimin

Phenyloxadiazolone Oxadiargyl, Oxadiazon

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Phenyloxazolidinedione Pentoxazone

Phenylpyrazole Fluazolate, Nipyraclofen, Pyraﬂufen-ethyl

Phenylpyrroledione Chlorphthalim, Cinidon-ethyl, Flumiclorac, Flumioxazin, Flumipropyn

Phenyltriazolinone Azafenidin, Bencarbazone, Carfentrazone-ethyl, Sulfentrazone

Phenyltriﬂuoromethylpyridazone Flufenpyr

Phenyltriﬂuoromethyluracil Benzfendizone, Butafenacil, Flupropacil, Saﬂufenacil, Tiafenacil

Triﬂuoromethylphenoxychlorobenzene Ethoxyfen

F1 Carotenoid Triﬂuoromethylphenoxybutyramide Beﬂubutamid 12 biosynthesis nhibitors

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Triﬂuoromethylphenoxypyridinecarboxamide Diﬂufenican, Flufenican, Picolinafen

Trifluoromethylphenyl aminopyridazone Metflurazon, Norflurazon

Triﬂuoromethylphenylfuranone Flurtamone

Triﬂuoromethylphenylpyridone Fluridone

Triﬂuoromethylphenylpyrrolidone Flurochloridone = Fluorochloridone

F2 Dioxocyclohexanecarbaldehyde Fenquinotrione, Ketospiradox, 28 (27) Mesotrione, Sulcotrione, Tefuryltrione, Tembotrione

Isoxazolecarbaldehyde Isoxachlortole, Isoxaﬂutole

Oxobicyclooctenecarbaldehyde Benzobicyclon, Bicyclopyrone

Pyrazolecarbaldehyde Benzofenap, Pyrasulfotole, Pyrazolynate, Pyrazoxyfen, Tolpyralate, Topramezone

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

F3 Phenoxynitroaniline Aclonifen 11

Triazolamine Amitrole

F4 Isoxazolidone Clomazone 13

G Enolpyruvylshikimate- Phosphonomethylglycinamide Huangcaoling 9 3-phosphate synthase inhibitors

Phosphonomethylglycine Glyphosate

H Glutamine Hydroxy methylphosphinoylhomoalaninamide Bilanafos 10 synthetase inhibitors

Hydroxy methylphosphinoylhomoalanine Glufosinate-ammonium

I Dihydropteroate Sulfanilylcarbamic acid Asulam, Carbasulam, 18 synthetase Fenasulam inhibitors

K1 Mitosis inhibitors Benzamide Propyzamide = Pronamide 3

Benzyl propionamide Tebutam = Butam

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Diﬂuoromethyltriﬂuoromethylpyridine Dithiopyr, Thiazopyr

Dinitroaniline Benfluralin = Benefin, Butralin, Chlornidine, Dinitramine, Dipropalin, Ethalfluralin, Fluchloralin, Isopropalin, Methalpropalin, Nitralin, Oryzalin, Pendimethalin, Prodiamine, Profluralin, Prosulfalin, Trifluralin Phosphoramidothioic acid Amiprophos, Butamifos, DMPA, Shuangjiaancaolin

Terephthalic acid Chlorthal

K2 Carbanilic acid Barban, BCPC, Carbetamide, 23 CEPC, Chlorbufam, Chlorpropham, CPPC, Propham, Swep

K3 Benzothiazolyloxyacetamide Mefenacet 15

Carbamoylmethylphosphorodithioic acid Anilofos, Piperophos

Chloroacetamide Acetochlor, Alachlor, Allidochlor = CDAA, Butachlor, Butenachlor, CDEA, Delachlor, Diethatyl, Dimethachlor, Dimethenamid-P, Ethachlor, Ethaprochlor, Metazachlor, Pethoxamid, Pretilachlor, Propachlor, Propisochlor, Prynachlor, S-metolachlor, Terbuchlor, Thenylchlor, Xylachlor Diphenylacetamide Diphenamid

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Naphthoxyisopropionamide Naproanilide, Napropamide

Phenyloxotetrazolinecarboxamide Fentrazamide

Phenyloxotriazolinecarboxamide Ipfencarbazone

Sulfonylisoxazoline Fenoxasulfone, Pyroxasulfone

Sulfonyltriazolecarboxamide Cafenstrole, Epronaz

Thiadiazolyloxyacetamide Flufenacet

Trifluoromethanesulfonanilide Mefluidide, Perfluidone

L Cellulose inhibitors Dichlorobenzonitrile Dichlobenil 20

Dichlorobenzothioamide Chlorthiamid

Isoxazolyl benzamide Isoxaben 21

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Phenyltriazolecarboxamide Flupoxam (28)

Fluoromethyltriazinediamine Indaziﬂam, Triaziﬂam (29)

M Oxidative Dinitrophenol Dinofenate, Dinoprop, Dinosam, 24 phosphorylation Dinoseb, Dinoterb, DNOC, uncouplers Etinofen, Medinoterb

N Fatty acid and lipid Phosphorodithioic acid Bensulide 8 biosynthesis inhibitors

Thiocarbamic acid Butylate, Cycloate, Di- allate = Diallate, Dimepiperate, EPTC, Esprocarb, Ethiolate, Isopolinate, Methiobencarb, Molinate, Orbencarb, Pebulate, Prosulfocarb, Thiobencarb, Tiocarbazil, Tri-allate = Triallate, Vernolate Dihydrobenzofuranyl sulphonate Benfuresate, Ethofumesate 16

O Synthetic auxins Chlorobenzoic acid 2,3,6-TBA, Chloramben, Dicamba, 4 Tricamba

Chlorooxobenzothiazolylacetic acid Benazolin

Chlorophenoxyacetic acid 2,4,5-T, 2,4-D, 3,4-DA, 4-CPA, MCPA

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Chlorophenoxybutyric acid 2,4,5-TB, 2,4-DB, 3,4-DB, 4-CPB, MCPB

Chlorophenoxyisopropionamide Clomeprop

Chlorophenoxyisopropionic acid 3,4-DP, 4-CPP, Cloprop, Dichlorprop-P, Fenoprop, Mecoprop

Chlorophenylacetic acid Chlorfenac = Fenac

Chlorophenylpropionic acid Chlorfenprop

Chloropicolinic acid Aminopyralid, Halauxifen, Clopyralid, Picloram

Chloropyridyloxyacetic acid Fluroxypyr, Triclopyr

Chloropyrimidinecarboxylic acid Aminocyclopyrachlor

Chloroquinolinecarboxylic acid Quinclorac, Quinmerac

P Auxin transport Phthalamic acid Naptalam 19 inhibitors

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Semicarbazonomethylnicotinic acid Diﬂufenzopyr

Z Unknown Organic arsenic CMA, DSMA, MAA, 17 MAMA, MSMA

Benzanilide Etobenzanid 27 (26)

Benzyl butyramide Bromobutide

Benzyldihydrooxazinone Oxaziclomefone

Benzyloxyoxabicycloheptane Cinmethylin

Benzylurea Cumyluron, Daimuron, Methyldymron

Carbamoylphosphonic acid Fosamine

Fluorenecarboxylic acid Chlorﬂurenol = Chlorﬂurecol

Table 9 (Continued)

HRAC Mechanisms of WSSA groups action Chemical families* Active ingredients† groups‡

Methyldithiocarbamic acid Dazomet, Metam = Metham

Pelargonic acid Oleic acid, Pelargonic acid

Phenyl pyridylthiocarbamate Pyributicarb

Pyrazolium Difenzoquat

*The position of substituents and heteroatoms of rings in the chemical structure are based on the majority of active ingredients within a chemical family. Thus, it is possible that such positions in a few active ingredients differ slightly from that shown in the chemical structure. †The italicised active ingredients approved for use or known to be used in at least one European Union country (EU Pesticides database available at: http://ec.europa.eu/sanco_pesticides/public/index.cfm?event=homepage&language=EN#). ‡Group numbers enclosed in parenthesis are the new numbers suggested by WSSA (2011) instead of the adjacent number out of the parenthesis or they are being suggested for the first time (such as group number 29). chemical structure of prothioconazole compared to opportunity for managing herbicide resistance in triazole compounds led Parker et al. (2011) to probe weeds. Including over 100 extra active ingredients with the biochemical basis of the demethylation inhibitor’s known chemical families, mechanisms of action and affinity to the target protein. Further investigation of herbicide groups opens up new opportunities for the fungicide interaction with the target protein researchers and farmers to design more flexible rota- revealed that prothioconazole interacts with CYP51 in tional herbicide programmes and to decrease the risk a novel way that is distinct from other azole fungicides of occurrence of herbicide (cross)resistance. As herbi- (Parker et al., 2011). Classification of active ingredients cides of chemical families within a mechanism of according to their chemical structure provides a way action play an important role in the evolution of cross- for the study of resistance in active ingredients with resistant weed biotypes, the replacements, additions similar chemical structure. Based on this study, all and omissions that have been adjusted in the present active ingredients in a chemical family have a same study should have promising consequences for herbi- moiety although being different from each other. As cide-based weed management strategies. the active ingredients within a chemical family have the same mechanism of action and moiety, thus they may have similar pattern of resistance. Nevertheless, Acknowledgements differences between the active ingredients within a The authors would like to express their appreciation to chemical family may result in more than one pattern the anonymous reviewers that critically reviewed and of resistance in that family (Table 8). significantly improved the quality of this manuscript.

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